It is established technology to disintegrate the pulp derived from a wood pulping mill into fibers, for example, to defibrate virgin pulp via a defibration device, e.g. hammer mill, grinding mill. The fibers are transported through conduits, usually moved by forced air, to an area adapted for fiber deposit and fibrous web formation. The very nature of air transport causes the tangling and clumping together of the fibers. Various devices are known to effect fiber deposit to attain control of fiber laydown and to gain a substantially uniform web thickness. These devices involve what may be called a sifting apparatus, such as an agitator means positioned above an apertured screen for causing fibers to pass through the apertures or openings in the screen to a receiving member, usually in the form of a moving wire or belt.
For example, a rotary impeller means may be provided to detangle and declump the fibers, and to distribute the fibers over a sifting screen, seeking a uniform deposition of fibers on a traveling perforated belt, known in the art as a "former wire." The impeller disposed within an open fiber distribution housing may rotate upon horizontal axes that are aligned in parallel to the plane of the forming wire. These axes extend transversely of the direction of "wire" movement.
One prior open fiber distributor housing having a cylindrical chamber with its arcuate bottom wall perforated for distributing fibers onto the forming wire uses, as the motive force for moving the fiber, air suction as well as a helically-bladed rotor with the rotor axis essentially coincident with the cylindrical chamber axis of curvature. This arrangement serves to distribute the fibers in close proximity to the screen and substantially evenly distributes them along the transverse length of the chamber. Air suction then causes the fibers to be drawn through the screen and be deposited on the forming wire. See, U.S. Pat. No. 4,627,806 [Johnson] issued Dec. 9, 1986.
Major concerns in the formation of fiber webs are achieving uniformity across the entire web which includes uniformity in basis weight, lift, entanglement, and resolving the difficulty in providing consistent fiber orientation for maximum cross-strength of the resulting web. Erratic production results are still experienced, as the web commonly experiences orientation of fibers in the machine direction due to the air suction. This results in loss of strength in the web in a cross-machine direction. Another, and equally more difficult obstacle to uniform web formation, is the frequent occurrence of fiber clumps or nits due to the air suction drawing small fiber clumps through the screen.
Prior air suction systems, long used to pull the collecting fiber through a sizing screen, such as standard air exhaust means, are plagued by the flow distortions created by fiber clumping and erratic aperture blocking in the sizing screen. This creates distorted fiber flowthrough patterns from the fiber distribution housing, and so markedly interferes with achieving a uniform depositing of fiber, a balanced loft and basis weight in the resulting web.
In the present invention, it is intended that the arcuate screen have a fiber deposition or "coating", fostering a positive pressure build-up in a closed fiber distribution housing, followed by the high frequency repetitive wiping and fiber clearing action by a high-RPM helically arranged blades of a rotor means. The building of positive pressure applied to the closed distributor housing, rather than air suction applied from below the former wire, is a chief factor in accomplishing randomized fiber flowthrough across the entire field of the machine. This action fosters a more uniform fiber descent through a vertically oriented duct means for preventing external influences upon the virtually free-falling fibers.
It is, therefore, a principle object of the invention to provide an improved air-laid, non-woven fibrous web making process, in terms of the varied sources of feedstock and reduced fiber waste in their conversion to formable fibrous web structures. It is another object of the invention to provide an air-laid, web making process which is better adapted to short production run applications, like for non-wovens which may be utilized in the premoistened and industrial wipe markets, and to enhance the inherent economic advantages of producing non-wovens from a variety fiber sources.
Still another object of the invention is to provide a process with a significantly reduced environmental impact, including energy conservation, by avoiding significant toxic chemical waste, vaporous pollutants, and by requiring markedly less process water elimination than used in conventional paper making. Yet another object of the invention is to provide a process for using fiber feedstocks from a variety of fiber sources (wood pulp, newsprint, telephone directories, office waste paper, synthetic fibers etc.), and effecting random fiber lengths that will ultimately yield non-wovens of acceptable fabric bulk and desired physical properties.
Other objects will appear hereinafter.